1. Field of the Invention
The present invention relates to a probe card for connecting a wafer to be measured with a measuring device in a semiconductor wafer testing device.
2. Description of the Related Art
Marked progress has been seen in the recent semiconductor manufacturing technology, including the progress of fine processing technology required for high density integration. For high density implementation as well as for suppression of heat generation and downsizing each elements, the current and voltage required for operation in the semiconductor devices are reduced year by year. Thus, the importance of microcurrent measurement has been recognized, and higher accuracies in microcurrent measurement are required in probe cards for connecting measuring devices and wafers.
Such a requirement is also present in the wafer process control testing. As a conventional testing method for process control, measurement chips referred to as TEG (Test Element Group) are formed at the same time as ordinary chips are formed on wafers for characteristic measurements. In such measurement, a probe card is used as an interface card between a measuring device and a wafer prober for moving and positioning a wafer to be measured, and is provided around its circular hole with a plurality of wafer contact needles also referred to as contact blades so as establish contacts with measuring terminals of the wafer.
In FIG. 10, a probe card is generally a circular disk 100 having a diameter from about 20 to 30 cm, with its central portion provided with an opening 102 through which contact needles or blades (not shown) can extend to contact with measuring terminals on a semiconductor wafer placed to be measured just under the probe card. Each wire 103 extends from each needle or blade located at the inner periphery toward the outer periphery where it is connected to a measuring device or the like. That is, a signal picked up from each terminal of a semiconductor wafer to be measured is introduced into the outer periphery of the probe card via each needle or blade, and is then sent to a measurement device from an external connection terminal 104 located on the outer periphery of the probe card. At that time, wires for connecting the semiconductor wafer to be measured with the measuring device are several tens in number and placed adjacent to one another. Guard patterns 105 formed with a conductor are located around the corresponding external connection terminals 104. In the example shown in the drawing, the number of external connection terminals or pins is forty eight (48). Such a probe card is also known as a personality board or interface card. See Japanese Utility Model Provisional Publication (JP-A) No. Showa 64-47042, and Japanese Patent Provisional Publication (JP-A) No. Heisei 8-330369.
In general, such a probe card has external contact terminals 104 at its outer periphery for connection with a measuring device. Each contact terminal 104 is composed of a planar conductor provided on a substrate surface of the probe card, on which, for example, a conductor contact needle, such as a contact pin member which comprises a conductive rod with a circular cross-section provided with a spring at its base and surrounded by a cylindrical member such that on application of appropriate force the rod is retracted and biased by a reaction force so as to establish electrical contact by pushing the tip of the rod against a conductor surface, with a mechanism to provide secured electric contact is pushed against the planar conductor surface of the probe card, thereby to connect with an external apparatus such as a measuring device. Further, each external contact terminal 104 has a pattern extension portion 106 near its inner periphery, and a corresponding planar conductor on the surface of the probe card extends inwardly. To the pattern extension portion one end of a coaxial cable 103 is connected, and the other end of the coaxial cable is connected with a base end of a contact needle which has the shape of the needle or blade as described above. Namely, the coaxial cable 103 extends in the air between the pattern extension portion and the contact needle. The needle or blade is attached to the inner periphery of the probe card and extends inwardly therefrom. Further, the tip of the needle or blade extending inwardly is connected to a predetermined terminal on a semiconductor wafer to be tested.
As mentioned above, in the field of testing semiconductor elements, testing appliances which can measure microcurrents smaller than the currently used level are required. Also, the measuring accuracy of femtoampere order is required for interface cards used for wafer probers. Major problems on developing testing devices with such high performance include leakage current between adjoining electric wires for connecting a testing device and a semiconductor to be measured and dielectric absorption occurring between such wires and dielectrics in a probe card substrate.
For example, the problem of dielectric absorption occurs due to dielectric absorption properties (absorption current) of the dielectric used as the probe card substrate. Generally, insulating materials show dielectric polarization when a voltage applied across two electrodes changes, and absorb a current gradually until the polarization process is completed. Therefore, even if a predetermined voltage is applied to a semiconductor wafer for current measurement, the current measurement can not be performed correctly for a certain time period and a waiting time is necessary until the current flow becomes stabilized. A waiting time is also necessary when the voltage supply is terminated because a discharge current flows out gradually. For conventional interface cards for wafer probers, it is not unusual that such a waiting time for measurement may be several tens of seconds until the dielectric absorption current is reduced to a femtoampere order. This is one of important problems in case of reducing the time required for the microcurrent measurement.
As the measuring accuracy of a femtoampere order is now required, the leakage current flowing through a dielectric material between adjoining wires has also become important.
Among the components on the probe card as mentioned above, portions of the external contact terminal and the pattern extension portion tend to be affected by the dielectric absorption and current leakage. The coaxial cable extending from each pattern extension portion runs in the air so that it is little influenced by the dielectric absorption or current leakage. As the needle portion, for example, a coaxial highly insulating needle can be used, and a shield wire surrounding the core wire of this needle can be connected with a guard. In addition, insulation between adjoining needles having a portion of the needle wire not covered with the shield wire is good because it is achieved by air which has the same dielectric constant approximately as that of vacuum. Also, the response time of the dielectric polarization is not an issue.
To address these problems caused by the external contact terminal, conventionally, a plurality of through-holes are formed from electrodes on the surface through the probe card substrate such that the periphery of the electrodes can be defined. One example of such technologies is described in Japanese Patent Provisional Publication No. Heisei 8-335754.
One problem in such a method is that a distortion tends to occur in the probe card as the number of through-holes is increases, and that the physical strength of the card degrades in or near the region of the through-holes. Even if the number of the through-holes is increased regardless of manufacturing difficulties and cost elevation, some leakage current through the dielectric between these through-holes still remains as a problem, and a dielectric loss can not be reduced to a desired level as a higher level of measuring accuracy is required.
It has been noted that there are variations in the dielectric and leakage current properties of each wire for each probe card. Therefore, even if the manufacturing process control is improved sufficiently, such variations in the dielectric and current leakage properties of each wire for each probe card would limit the accuracy of current measurements. For example, in case of a currently used probe card with 48 pins after application of a voltage of about 10 volts, the leakage current 10 seconds after that voltage application of most pins is about 0.3xc3x9710xe2x88x9213 A. However, such a leakage current of other specific pins becomes about 1 to 2xc3x9710xe2x88x9213 A.
It is an object of the present invention to reduce a measuring waiting time resulted from dielectric absorption and decrease a steady-state leakage current so as to enhance accuracy of measuring microcurrents or fluctuations of them. It is another object of the present invention to reduce variations of properties of each pin or each probe card.
In light of the problems described above of the prior art, the present invention relates to a structure in which an external connection terminal for use in a probe card is surrounded by conductors.
The present invention provides a probe card which comprises a substrate and an external connection terminal disposed on the substrate, wherein the external terminal is separated from a substrate body via conductors attached to the substrate.
The conductors surrounding the external connection terminal in the present invention is preferably connected to a guard terminal, more preferably to an active guard terminal.
The conductor attached to the substrate surrounds the external connection terminal in the substrate. Assuming that the conductor has a box-like configuration, the bottom face of the conductor is located below the external terminal in the substrate, and the four side faces are located in the substrate and surround the external connection terminal from all quarters. The term xe2x80x9cin the substratexe2x80x9d does not necessarily mean that the conductor is embedded in the substrate. That is, at least a portion of each conductor should appear from the substrate surface and may protrude therefrom. Further, when the substrate surface is recessed or notched, the conductor may be exposed in the recessed or notched portions of the substrate or protrude in the air.
In such a construction of the present invention, the microcurrent properties of femtoampere order can be enhanced so that the measuring accuracy can be improved. The waiting time resulted from the instability of the current due to the dielectric absorption can also be reduced. In addition, the substrate can include other electrical networks which could not be included in the substrate so far because of their possibility of degrading the microcurrent properties. Because the probe card of the present invention can be made in general in a planar structure (although it can have three-dimensional structures), it can be handled easily and reduce the cost for storage or transportation. Moreover, the present invention is compatible with currently available probe cards.
The substrate may have a mono-layered structure, but preferably it has a multi-layered structure. In a preferred embodiment, for example, conductive wires can be provided among layers, and via-holes or through-holes can be formed in a multi-layered substrate by one of commonly known technologies for manufacturing multi-layered substrates.
The probe card of the present invention can be manufactured in accordance with the following procedure,while it is not limited by any manufacturing processes. The external connection terminal surrounded by conductor can be produced, for example, by forming a recess in a substrate, providing a box-like external connection terminal portion in which an external connection terminal is formed on the top surface, and a conductor material is disposed on the side surfaces by plating or the like, and fitting the box-like external connection terminal portion in the recess. Alternatively, the external connection terminal can be produced by forming a recess in a substrate, disposing a conductor material in the recessed portion by plating or the like, and fitting or adhering in that recess a member composed of a box-like dielectric and an external connection terminal provided thereon. Otherwise, in case of a multi-layered substrate, the external connection terminal surrounded by conductors can be produced by placing a conductor pattern on an inner layer located below the external connection terminal, cutting a pattern surrounding the terminal and reaching the inner layer after lamination, and applying a conductor material into the cut pattern.